1. Field of the Invention
This invention relates to catalytically promoted chemical processes. More particularly, it relates to chemical processes conducted in the presence of a fixed bed of catalyst. This invention especially relates to a catalytic chemical process wherein the catalyst is provided in a multiplicity of fixed beds.
2. Description of the Prior Art
A myriad of chemical reactions are performed commercially each year in the chemical, petroleum, petrochemical and related industries. Many of these reactions are catalytically promoted by homogeneous or hetergeneous catalysts. The solid catalyzed fluid phase reactions are the most important and the most commonly encountered in today's industrial processes. Although for many years solid catalysts were employed in fixed beds, the development of gas oil cracking during World War II for the production of 100 octane aviation gasoline employed a solid catalyst in the form of a fluidized bed. Within a few years, the fluidized bed became the preferred means for conducting many industrial chemical processes. Despite the widespread use of fluidized catalyst beds, fixed beds of catalyst are still employed in a substantial number of chemical processes today.
In fixed bed processes, the activity of the catalyst in the bed usually declines with use, often because metallic materials in the feedstock or carbonaceous materials formed as a by-product in the reaction interfere with the effectiveness of the catalyst. It is usually necessary to periodically terminate the reaction in the catalyst bed and to either replace or regenerate the catalyst.
The variety of fixed catalyst beds which have been provided over the years has been limited only by the resourcefulness of the designer, the fabricator and the building contractor. In its simplest form a single fixed bed reactor is employed. The attendant deficiencies of this operation are manifest. Taking the catalyst bed off line often results in sub-standard products which must be discarded or re-processed. When the reactor is out of service while the catalyst is being replaced or regenerated, no product is being produced. Downtime is further extended during purging of the bed which is often necessary both before and after the regeneration. In addition, when the fixed bed is returned to service, the product produced during the initial on-stream period often fails to meet required quality standards.
Some of the problems encountered with single bed reactors have been alleviated through the use of a number of fixed bed reactors. U.S. Pat. No. 3,392,002 of Hamilton et al discloses a plurality of catalyst containing reactors which are interconnected so that they may be arranged in a series with any of the reactors occupying any position from first to last in the series. The reactors are also connected so that any of the reactors may be isolated from the series to permit regeneration of the catalyst therein. The complete flexibility provided in this system permits either parallel or series flow to be employed. The piping system here is an extremely complex system of manifolds involving numerous valves and crossovers. This operating flexibility is obtained at a very significant investment in valves and piping. U.S. Pat. No. 3,142,545 of Raarup et al addresses the investment problem when providing complete flexibility with multiple reactor systems by limiting the number of possible permutations and combinations through a simplified piping and valving arrangement. Although this system does not permit complete flexibility there is little sacrifice in operating efficiency. In a five reactor system, seventeen different flow arrangements are possible with this piping and valving. The flow through the reactors is series flow with parallel flow provided through two reactors in some particular arrangements. Each reactor can be segragated for regeneration.
U.S. Pat. No. 2,873,176 of Hengstebeck discloses a multiple reactor system where the processing of the feedstock is terminated and all of the reactors are regenerated. During the regeneration in Hengstebeck no product is produced. Following regeneration, the system is brought back onstream with the usual problems attendant during start up in a single reactor system.
Many multiple bed systems operate with complete parallel flow, e.g., U.S. Pat. Nos. 2,310,244 of Lassiat and 3,128,242 of Bergstrom et al., but most employ a serial flow pattern, e.g., U.S. Pat. Nos. 1,867,841; 2,873,176; 3,142,545; 3,392,002 and 4,259,294. Multiple bed reactor systems often employ the swing reactor concept wherein one reactor is removed from service for regeneration and a freshly regenerated reactor is simultaneously returned to service. In U.S. Pat. Nos. 1,867,841 of Joseph and 4,259,294 of Van Zijll Langhout et al. the spent reactor removed is the first reactor in the series and the reactor being returned to service is brought onstream as the last in the series. U.S. Pat. No. 3,142,545 of Raarup et al. teaches the use of a swing reactor in a reforming process. Since the catalyst in the several beds does not age uniformly because of the number of competing reactions taking place, it is not always the first or the last in the series which contains the most deactivated catalyst. The swing reactor is therefore brought onstream as a replacement for whichever of the several reactors requires regeneration. Although the first reactor in the series is always the one removed for regeneration in the multi-reactor process taught in U.S. Pat. No. 3,392,002 of Hamilton et al, the swing reactor is brought onstream as the second in line because of the particular operating sequence employed. In all four of these patents, however, the swing reactor is held in reserve after it has been regenerated and is returned to service only when one of the other reactors requires regeneration. There is no suggestion in the prior art of placing an out-of-service reactor back onstream as soon as the deactivated catalyst has been regenerated or replaced.
It is an object of this invention to provide a process for catalytic conversion with a slowly deactivating catalyst.
It is another object of this invention to provide a catalytic conversion process with a slowly deactivating catalyst wherein the equipment investment is minimized.
It is a further object of this invention to provide a process of catalytic conversion with a slowly deactivating catalyst in a series of fixed bed reactors wherein the offstream time for each reactor is minimized.
It is yet another object of this invention to provide a process of catalytic conversion with a slowly deactivating catalyst in a series of fixed bed reactors at a minimum capital investment.
These and other objects will be achieved by practicing the invention disclosed hereinafter.